Mercury MESSENGER Launch Postponed Until Tuesday

Thunderstorms and the threat of lightning early today forced
NASA officials to scrub their launch of the agency's first space probe to
Mercury in 30 years.

The poor weather, an expected offshoot of Tropical Storm
Alex churning off the eastern U.S. coast, delayed the Mercury-bound MESSENGER
spacecraft's launch from Cape Canaveral Air Force Station in Florida for at
least 24 hours. Thick cloud cover also factored into the scrub decision.

The launch attempt was officially aborted at 2:11 a.m. EDT
(0611 GMT) during a scheduled hold with just four minutes remaining in the countdown.
The spacecraft was originally set to ride a Delta 2 rocket into space at 2:16:11
a.m. EDT (0616:11 GMT) and had a 12-second launch window to make the space shot.

Pad crews are now working to launch MESSENGER Tuesday at
2:15:56 a.m. EDT (0615:56 GMT) - also with a 12-second window - when weather
conditions are expected to be more favorable. The mission itself has a 12-day
launch window starting Aug. 2 in order to reach Mercury.

MESSENGER, an acronym for MErcury Surface, Space ENvironment,
GEochemistry, and Ranging, is the first NASA spacecraft to Mercury since
Mariner 10, which swung by the planet in 1974. It is expected to pick up where
the Mariner left off, the first step of which is filling in the gaps of a global
map of Mercury that is currently only half complete.

"Here, we've got Mercury so close to us in the solar
system and we've only seen one side of it," explained Ralph McNutt, a MESSENGER
science team member with the Johns Hopkins University Applied Physics
Laboratory, during the countdown.

Researchers also hope MESSENGER will answer questions about
Mercury's above average density for its size, as well as its composition,
surface and magnetic field. The spacecraft will take about seven years to reach
Mercury, swinging by Earth, Venus and Mercury itself before entering orbit
around March 2011.

Weather difficulties expected

Weather officials at Cape Canaveral were aware that poor weather
conditions could affect MESSENGER's launch, and estimated a 30 percent chance
that the space shot could be delayed.

"While everyone here is looking forward to the next seven
years, I'll be very happy to get through the next 36 hours," said Joel
Tumbiolo, U.S. Air Force Delta 2 weather officer, during a prelaunch press
briefing on July 31.

While the Tuesday launch date also carries a 30 percent risk
of weather violations, launch officials said that regional thunderstorms should
largely be confined to daylight hours when tower roll back procedures are
scheduled. The lightning conditions threatened by clouds from Tropical Storm
Alex should not be a factor during the countdown, they added.